A 77-year-old man was found unresponsive in Kealakekua Bay near the Captain Cook Monument.
The incident happened at around 10:19 a.m. today.
Fire officials said Holua Kai found one of their guests face down in the water. He was brought on board where crew members began CPR/AED.
The Holua Kai snorkeling vessel brought the man to Keauhou Boat Ramp where fire personnel took over.
The man was transported to Kona Community Hospital.
A cardiac event may have led to the drowning, fire officials said.